The invention relates to a turbocompound unit as well as to a method for providing such turbocompound unit. More specifically the present invention relates to a turbocompound unit having a sealing arrangement for preventing oil from escaping from a bearing housing to a diffuser duct.
The invention can be applied in heavy-duty vehicles, such as trucks. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other vehicles for which the provision of a turbocompound unit is advantageous such as buses and construction equipment.
A turbocompound unit is a vehicle component used for recovering a part of the energy of the exhaust gas flow and to convert that energy into a rotational movement of a shaft. The rotational movement of the shaft is transferred as a torque increase to the crankshaft of the engine of the vehicle. Normally, the turbocompound unit has a shaft wherein a turbine wheel is arranged at one distal end. When the internal combustion engine is running exhaust gas will flow into the turbocompound unit and cause the turbine wheel to rotate. Hence, the shaft of the turbocompound unit will rotate accordingly. The opposite end of the shaft is provided with a gear wheel which meshes with additional gears for causing a rotational connection between the shaft and the crankshaft. When the shaft is rotating due to exhaust gas flowing through the turbocompound unit, the rotational energy of the shaft will be transferred to the crankshaft as a torque increase.
The use of turbocompound units has proven to provide significant advantages on driving economics as well as on the environment the energy recovery from the exhaust gas flow will in fact reduce the fuel consumption of the vehicle.
The turbine shaft is supported in a bearing housing for allowing the turbine shaft to rotate relative the housing. In order to minimize hot gas inflow from the gas path into the bearing housing as well as to prevent oil leakage in a reverse direction, sealing rings are used to seal between the static bearing housing and the rotating turbine shaft. As the static pressure level downstream the turbine wheel in some operating modes can be lower than the pressure inside the bearing housing a buffer air pressure is needed to prevent oil leakage.
It is known for example from document DE 10 2005 047 216 A1 to seal the turbine shaft by means of pressurised air. The pressurised air is supplied to a region of the shaft that is axially delimited by two sealing elements. This solution is relatively complex, and it requires reliable supply of pressure controlled air from an air compressor, as well as two high performance sealing elements. There is thus a need for a simplified sealing arrangement for a turbocompound unit, where the above mentioned disadvantages are removed.
It is desirable to provide a turbocompound unit overcoming the above mentioned drawbacks of prior art units.
By the provision of a turbocompound unit in which a sealing arrangement is pressurized by using exhaust gas from the collector it is possible to maintain a positive air flow into the bearing housing during the entire operation cycle.
According to an aspect, a turbocompound unit is provided. The turbocompound unit comprises a bearing housing and a turbine shaft being mutably supported in the bearing housing, wherein one end of the turbine shaft is provided with a turbine wheel. The turbocompound unit further comprises a diffuser duct in which the turbine wheel is arranged to rotate, an exhaust collector extending from the diffuser duct to an exhaust outlet, and a sealing arrangement positioned in the vicinity of the turbine wheel for preventing oil from escaping from the bearing housing to the diffuser duct. The exhaust collector forms part of a buffer gas duct that is arranged to supply exhaust gas from the exhaust collector to the sealing arrangement for pressurizing the sealing arrangement.
According to another aspect, a turbocompound unit is provided. The turbocompound unit comprises a bearing housing and a turbine shaft being rotatably supported in the bearing housing, wherein one end of the turbine shaft is provided with a turbine wheel. The turbocompound unit further comprises a diffuser duct in which the turbine wheel is arranged to rotate, an exhaust collector extending from the diffuser duct to an exhaust outlet, and a sealing arrangement positioned in the vicinity of the turbine wheel for preventing oil from escaping from the bearing housing to the diffuser duct. A buffer gas duct leads into the exhaust collector, whereby the buffer gas duct is arranged to supply exhaust gas from the exhaust collector to the sealing arrangement for pressurizing the sealing arrangement.
The following embodiments provide advantages for both aspects presented above.
According to an embodiment the exhaust collector forms an annular flow path for the exhaust gases whereby it allows a part of the buffer gas duct to be formed at a specific angular position relative the exhaust outlet. The angular position may thus correspond to the angular position at which the exhaust gas pressure is at its maximum.
According to further embodiment the buffer gas duct extends from a buffer gas inlet arranged at the outer periphery of the exhaust collector. Hence the gas inlet is in fluid communication with the volume inside the exhaust collector and the buffer gas duct may be constructed to extend from the gas inlet without interfering with the volume inside the exhaust collector.
According to a yet further embodiment the buffer gas inlet is arranged 170°-190° from the exhaust outlet, preferably approximately 180° from the exhaust outlet. The buffer gas inlet, is thus arranged at a circumferential position of 170°-190°, and preferably 180° measured from the circumferential position of a center of the exhaust outlet. This angular position has been proven to correspond to the maximum pressure inside the exhaust collector.
According to an embodiment the exhaust collector has an axial extension and the buffer was inlet may be positioned centrally along the axial extension.
According to an embodiment the buffer gas duct comprises a channel inside a wall of the exhaust collector. This is advantageous in that the need for additional components, such as pipes, fittings, etc is removed.
According to a further embodiment the diffuser duct comprises an outer diffuser duct wall and an inner diffuser duct wall extending essentially parallel to the outer diffuser duct wall, and wherein the inner and outer diffuser duct walls jointly define at least a part of the buffer gas duct. Hence the volume formed between the inner and outer diffuser duct wall may be used to form part of the buffer gas duct.
According to a yet further embodiment the sealing arrangement comprises an annular pressure cavity surrounding the turbine shaft, and wherein the annular pressure cavity is in fluid connection with the buffer gas duct. The pressure cavity thus forms an annular sealing since the high pressure inside the cavity is always maintained due to the supply from the exhaust collector via the buffer gas duct.
According to an embodiment the annular pressure cavity is arranged between two seals being spaced-apart axially along the turbine shaft, and at least one of the seals may be a labyrinth seal. Hence the pressure inside the cavity will be maintained at a higher level than inside the bearing housing.
The sealing arrangement may further comprise an annular buttes cavity surrounding the turbine shaft, and wherein the annular buffer cavity is spaced-apart from the annular pressure cavity in an axial direction. The annular buffer cavity is preferably arranged on the turbine shaft gear wheel side of the annular pressure cavity, whereby dynamic behaviour of oil splash etc from the bearing housing will be accommodated by the annular buffer cavity. The risk of oil leakage into the diffuser will thus be further decreased.
According to a yet further embodiment the annular buffer cavity is arranged between two seals being spaced-apart axially along the turbine shaft, and wherein one of the two seals is sealing the annular pressure cavity from the annular buffer cavity. By allowing the annular pressure cavity and the annular buffer cavity to share a common sealing the complexity of the construction is reduced.
The annular buffer cavity may in some embodiments be formed by a seal land being supported by an oil slinger and/or a seal ring carrier. The seal land may comprise a through hole for draining fluid entering the annual buffer cavity.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.